Re: a difficulty about fit function

Hi,

I'm not sure I understood correctly your question, but a description of the landau distribution can be found here:

http://en.wikipedia.org/wiki/Landau_distribution

To look at implementation code in ROOT, have a look here:

$ROOTSYS/math/mathcore/src/PdfFuncMathCore.cxx

and

$ROOTSYS/math/mathcore/inc/PdfFuncMathCore.h

There are only two parameters which are sigma and x0 (most probable value). David

Fengchu Zhou wrote:
> Hi all
> A stupid question.
>
> I want to get the exact expression of the equation of the landau
> distribution in the ROOT fit gr1->Fit(landau,"R").
> When I find in the file in this path
> /Root/v5-23-02/math/mathcore/src/TMath.cxx
>
> i find the function in the TMath.cxx
> Double_t TMath::Landau(Double_t x, Double_t mpv, Double_t sigma, Bool_t norm)
>
>
> But in this function contain the expression is puzzle me . I do not know
> the meaning of this sentence:
> Double_t den = ::ROOT::Math::landau_pdf( (x-mpv)/sigma );
>
> And I can not find the landau_pdf in the file Math.h
>
> So can anyone kindly tell me the exact expression of the landau function?
> And the fit par[n] location in this expression.
> Like gauss funtion form:
> f(x)= par[1]*exp(1/par[3] *(x-par[2])^2) where the par[n] is the fit
> parameter
>
>
> Best regard,
> Fengchu
>
>
>
>
Received on Thu Oct 15 2009 - 14:02:00 CEST